The object of the invention is a spring for use in spring cores according to the object of U.S. Pat. No. 4,817,924 going back to the same applicant. Springs of this type have proven themselves and are superior to the looped Bonnell springs because they achieve the same spring force without loops and thus require less wire.
It was observed that when a spring of that type was used, a relatively high number of springs per surface unit of a mattress body must be used because the surfaces in the area of the upper and the lower end rings of the individual springs are relatively narrow.
This means that a relatively large number of such springs must be used per surface unit of a mattress, which is associated with increased production costs and an increased cost of installation.
Furthermore, during use of the proven spring according to U.S. Pat. No. 4,817,924, it has turned out that in many cases undesirable rubbing noises have occurred when the spring arrangement is subjected to a load. This is due to the fact that the upper end ring lies practically flush with certain leg parts over the round wound spring coil part starting below it, as a result of which parts of the upper end ring strike the spring coil part lying below it when a load is applied to the spring arrangement and may generate an undesirable rubbing noise.
Furthermore, the individual support surface of the known spring can also be improved because the relatively small surfaces of the upper and lower end rings of the spring had the disadvantage that the spring moved as one whole part without resulting in tilting or twisting of the end rings for the purpose of matching to the body surface lying on top.